Different Genetic Possibilities within the Balance Theory 443 



missing is only a physiological condition of the male gametes enabling 

 them to function. In insects we have some knowledge what this 

 means, namely, the need of a hormone-like stimulus for sperm motility. 

 In Lepidoptera this substance is secreted in the female organs where 

 sperm is stored and, therefore, is certainly not a part of male sex 

 determination. Growth of the gonads in insects is also dependent upon 

 a known hormone. "These physiological features have clearly nothing 

 to do with sex determination as such, but act in a definite physiological 

 way upon the genetically determined sex cells. Thus I conclude that 

 the right section of the Y in Melandriiim does not have a partial 

 function in sex determination, but controls some physiological action 

 upon the fully determined male sex cells that is needed for finishing 

 their cycle. The left end and the middle part of the Y remain alone 

 for assaying. 



According to Westergaard, the left segment of the Y contains only 

 genes for the suppression of the female organs, because its absence 

 results in fully developed hermaphrodite flowers. From this the in- 

 ference is made that the middle segment contains the male deter- 

 miners for anther development. This conclusion cannot stand close 

 scrutiny, if all the facts are taken into account: subandroecious and 

 subgynoecious flowers and the Ustilago effect. I can only conclude that 

 the left and middle sections of the Y contain powerful suppressors of 

 the female primordia, so powerful that they win out even in the 

 presence of as many as three F-carrying X-chromosomes, that is, a 

 powerful shift of the F/M balance in favor of F. The anthers are 

 clearly always formed when only one X-chromosome is present, a bal- 

 ance F(X)/M( autosome) strongly in favor of M. There is absolutely 

 no need and no proof for assuming male determiners to be in the 

 Y-chromosome, but the suppressors of the female anlagen may also be 

 called enhancers of maleness, if we realize that the dioecious plants 

 are actually monoecious with suppression of the anlagen of one sex. 



Thus the problem of monoecism enters. Westergaard himself has 

 emphasized that it must not be forgotten that the only two dioecious 

 species of Melandrium must have been derived from monoecious ones. 

 This is indeed a decisive point. If they are basically monoecious with 

 a secondary suppression of female organs in the male (and vice versa), 

 and these organs, as we have seen, can reappear in definite genotypes, 

 the basis of sex determination is a F/M balance which is very near 

 equality and is shifted only inadequately by the '1X-2X mechanism. 

 This means that MM is only a little superior to one F, while MM is 



